Improve formula syntax docs for from_string method

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

src/frequenz/sdk/timeseries/logical_meter/_logical_meter.py

@@ -94,14 +94,17 @@ def start_formula(
     ) -> Formula[Quantity]:
         """Start execution of the given formula.
 
-        TODO: link to formula syntax.
+        Formulas can have Component IDs that are preceeded by a pound symbol("#"),
+        constant values and these operators: +, -, *, /, (, ).
 
-        Formulas can have Component IDs that are preceeded by a pound symbol("#"), and
-        these operators: +, -, *, /, (, ).
+        These functions are also supported: `COALESCE`, `MAX`, `MIN`.
 
         For example, the input string: "#20 + #5" is a formula for adding metrics from
         two components with ids 20 and 5.
 
+        A more detailed description of the formula syntax with examples can be found
+        [here](https://github.com/frequenz-floss/frequenz-microgrid-formula-engine-rs?tab=readme-ov-file#formula-syntax-overview).
+
         Args:
             formula: formula to execute.
             metric: The metric to use when fetching receivers from the resampling actor.